1. Field of the Invention
The present invention relates to a cylinder block and a manufacturing method thereof.
2. Description of Related Art
As for a cylinder block, the following technique is known: a slit is formed between adjacent cylinder bores, and cooling water flows through the slit, thereby improving cooling power of the cylinder block. Japanese Patent Application Publication No. 2012-097719 (JP 2012-097719 A) describes such a cylinder block in which a slit is formed between adjacent cylinder bores so as to flow cooling water therebetween. Further, in JP 2012-097719 A, a cover is molded by performing laser beam welding while supplying metal powders to an upper part of the slit, thereby improving strength of the cylinder block.
The technique to mold a cover from metal powders, as described in JP 2012-097719 A, takes time for machining, and thus, has poor productivity. Therefore, it is preferable to weld a plate-shaped cover to a cylinder block by laser beam welding, from the viewpoint of productivity. However, when a plate-shaped cover is welded to a cylinder block by laser beam welding, gas generated from a welded portion of the cylinder block might remain in the welded portion as a defect such as a pin hole or a blowhole. This problem tends to occur markedly as the cover is thicker, that is, the laser beam welding is performed more deeply.